Hi there, I consulted one of the p2 developers about this. While he isn't aware of any plugins that specifically focus on making network use of P2 better, there are some hooks/filters in the theme that you might be able to use to build it out if you really wanted to. Mentions are built into P2, and there are some filters (e.g. p2_user_suggestion) which could be used to control the list of suggested users.

Waiting for o2 is probably a better option if you're not in a hurry and aren't able to invest the development time. The first release of o2 will likely focus more on single-post installs, with some network features to be released as a downloadable o2 package at some point down the road.